/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		System.out.println(x(2, 3));
		System.out.println(x(100, 5));
		System.out.println(x(42, 0));
		System.out.println(x(0, 3));
		System.out.println(x(0, 0));
	}
	
	public static int x(int n, int p)
	{
		return -((p%2<1) ? p*p/2+p : p/2 * (p+2) + 1) + n - p*n;
	}
}